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A study of possible extra-framework cation ordering in Pbca leucite structures with stoichiometry RbCsX2+Si5O12 (X = Mg, Ni, Cd)

Published online by Cambridge University Press:  08 February 2019

Anthony M. T. Bell Open the ORCID record for Anthony M. T. Bell [Opens in a new window]  and
C. Michael B. Henderson
Anthony M. T. Bell*
Affiliation:
Materials and Engineering Research Institute, Sheffield Hallam University, Sheffield, S1 1WB, UK
C. Michael B. Henderson
Affiliation:
School of Earth and Environmental Sciences, University of Manchester, Manchester, M13 9PL, UK
*
a)Author to whom correspondence should be addressed. Electronic mail: Anthony.Bell@shu.ac.uk
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Abstract

Leucites are silicate framework structures with some of the silicon framework cations partially replaced by divalent or trivalent cations. A monovalent extraframework alkali metal cation is also incorporated to balance the charges. We have previously reported Pbca leucite structures with the stoichiometries Cs2X2+Si5O12 (X = Mg, Mn, Co, Ni, Cu, Zn, Cd) and Rb2X2+Si5O12 (X = Mg, Mn, Ni, Cd). These orthorhombic leucite structures have all the silicon and non-silicon framework cations completely ordered onto separate crystallographic sites. This structure has five distinct Si sites and 1 X site; there are also two distinct sites for the extra-framework Cs or Rb. We have recently synthesised leucite analogues with two different extra-framework cations, these have the stoichiometry RbCsX2+Si5O12 (X = Mg, Ni, Cd). The initial Rietveld refinements assumed 50% Cs and 50% Rb on each of the two extra-framework cation sites. The refined structures for X = Ni and Cd have (within error limits) complete extra-framework cation site disorder. However, for X = Mg there is partial ordering of the extra-framework cation sites, the site occupancies are:- Cs1 0.37(3), Rb1 0.63(3), Cs2 0.63(3), Rb2 0.37(3).

Keywords

X-ray powder diffractionRietveld refinementsilicate framework minerals
Type
Technical Articles
Information
Powder Diffraction , Volume 34 , Supplement S1 , September 2019 , pp. S2 - S7
Copyright
Copyright © International Centre for Diffraction Data 2019 

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References

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